1. Field of the Invention
The present invention relates to a semiconductor device that has a circuit including a thin film transistor (Hereinafter, TFT) and a method of manufacturing the semiconductor device.
The semiconductor device indicates general devices that are able to function with utilizing characteristics of semiconductor, and includes all of a liquid crystal display device, a display device (an EL display device) which has a self-light emitting element represented by an electroluminescent (Hereinafter, EL) element, a semiconductor circuit, and an electronic apparatus using those as parts.
2. Description of the Related Art
Recently, attention has been paid to techniques of manufacturing a TFT with using a thin semiconductor film (a thickness on the order of several to several hundreds nm) formed on an insulating surface of a substrate. It is expected that the TFT be widely applied to electronic devices, and rapid development is required for a switching element for driving a liquid crystal display device or an EL display device.
In a display device, attention is paid to an active matrix display device in which, in order to obtain an image with a high quality, pixel electrodes are arrange in a matrix shape and a switching element connected to each of the pixel electrodes is driven to perform displaying. Above all, an EL display device that has a pixel using an EL element that is a self-light emitting element is expected as a display device in the next generation, instead of a liquid crystal display device.
An EL element has an EL layer formed to be sandwiched between first and second electrodes, and electric current generated between the first and second electrodes to obtain emission of light for performing display of an image. There are given advantages that the device is lighter, thinner and more miniaturized since a backlight as used in a liquid crystal display device is unnecessary, a view angle is wide, and smooth display of an animation is obtained due to a quick response speed.
As a means for realizing a color display in an EL display device, there may be given a means in which an EL material for emitting light of each of red (R), green (G), blue (B) is used to form each light emitting portion, or a means in which an EL element for emitting light of a single color such as white or blue is used and emitted light is made to pass through a color filter or a color conversion layer for obtaining emission of light of each of RGB.
A color filter generally used for a display device has coloring layers 601 to 603 respectively corresponding to R, G, and B and a light-shielding layer 604 as shown in FIGS. 6A to 6C, and absorbs a part of light irradiated to the coloring layers and transmits the other part of the light to extract light of R, G, and B. The light-shielding layer 604 is generally formed of a film such as a metal (such as chromium) film or an organic film containing a black pigment, and may be provided right between adjacent pixels as shown in FIG. 6A or in a stripe-shape as shown in FIG. 6B. In the case that pixels is arranged in a delta arrangement, another means may be employed.
FIG. 6C shows a section along D–D′ in FIG. 6A or 6B. After the light-shielding layer 604 and the coloring layers 601 to 603 are formed on a substrate 651, a planarization film 652 may be provided in order to perform planarization of the surface. In addition, it is possible to use the planarization film 652 as a barrier layer against an impurity included in the coloring layers 601 to 603.
It is noted on a takeout direction of light emitted from an EL element that there is bottom-emission called in the case of taking out of a side of a substrate that has a TFT formed as shown in FIG. 4A while there is top-emission called in the case of taking out of a side of an opposing substrate as shown in FIG. 4B
In the case of forming a color filter, a position for forming is different in accordance with the takeout direction of emitted light. In the case of the bottom-emission, as shown in FIG. 4A, it is necessary that coloring layers be provided near a TFT substrate 400 rather than a pixel electrode 410 to form a color filter. That is, processes proceed in order of forming a TFT 402, forming a wiring 404, forming coloring layers 406 to 408, forming the pixel electrode 410, forming an EL layer 412, forming an opposing electrode 413, and sealing with an opposing substrate 401. In the case of the top-emission, as shown in FIG. 4B, coloring layers 459 to 461 are provided at a side of an opposing substrate 451 to form a color filter since the emitted light is obtained from a side of an opposing electrode 458. That is, the process for forming the color filter is independent of ones for a TFF substrate 450.
When a color filter is formed at the side of the TFF substrate like the case of the bottom-emission, there are problems that it is impossible that coloring layers themselves withstand a temperature of heat treatment in a later process and impurities in the coloring layers diffuse due to heat to have a TFF contaminated. Therefore, it is necessary to provide barrier layers 405 and 409, represented by a film such as a silicon nitride film, above and below the portion in which the coloring layers are formed. In the case of the top-emission, on the other hand, it is suitable that there is no necessary of worrying about the above-mentioned problems since it is possible to form a color filter independently of processes for the TFF substrate.